The present invention relates to a displacement control apparatus for a variable displacement compressor, a displacement control method and a compressor module.
A typical refrigerant circuit of a vehicle air conditioner includes a condenser, an expansion valve, an evaporator and a compressor.
Variable displacement swash plate type compressors are widely used in vehicle air conditioners. Such compressors include a displacement control mechanism, which operates to maintain the exit pressure of an evaporator or the suction pressure Ps of a compressor associated with the exit pressure at a predetermined target value (set pressure). The exit pressure of an evaporator or the suction pressure Ps of a compressor associated with the exit pressure reflects the magnitude of the cooling load. The variable control mechanism controls the exit pressure of the evaporator or the suction pressure Ps to adjust the inclination angle of the swash plate of the compressor, which adjusts the displacement of the compressor.
The variable control mechanism includes an internal control valve and an external control valve. The internal control valve has a pressure sensing member such as a bellows or a diaphragm. The valve opening degree is adjusted by sensing the exit pressure of the evaporator or the suction pressure Ps of the compressor with the pressure sensing member so that the valve body is positioned accordingly. The pressure in a crank chamber, which accommodates the swash plate, is adjusted by the valve opening degree. The inclination angle of the swash plate is determined by the pressure in the crank chamber. A simple internal control valve has only a single set pressure, and such a simple control valve cannot perform complex control for power consumption.
Such compressors are usually driven by vehicle engines. Among the auxiliary devices of a vehicle, the compressor consumes the most engine power. Accordingly, under exceptional conditions, for example, when the vehicle is accelerating or moving uphill, all available engine power needs to be used for moving the vehicle. To reduce the engine load, the compressor displacement must be minimized.
Japanese Unexamined Patent Publication No. Hei 10-278567 discloses an external control valve in which the valve opening degree can be controlled by external electric signals. A variable displacement compressor having the external control valve is able to minimize the discharge displacement of the compressor by changing the opening degree of the external control valve.
The power that the compressor actually consumes, or the load torque Tr of the compressor, varies greatly in accordance with changes in the suction pressure Ps and the discharge pressure Pd of the compressor. To prevent the engine from stalling even if the required load torque Tr of the compressor is increased, it is necessary for the compressor to be driven at high speed (over a predetermined value) at all times. However, this increases the power that the compressor consumes.
To reduce the power that the compressor consumes, a controller that controls the engine estimates the load torque Tr. The engine output torque Treng, which is the total torque of an engine, is a value obtained by adding the required load torque Tr of the compressor to the torque necessary for vehicle travel. When all available engine power needs to be used for moving the vehicle, the engine controller is able to give priority to moving the vehicle using this torque data.
The load torque Tr of the compressor has been estimated by the use of an experimentally created map. However, since the load torque Tr of a compressor is different depending on the refrigerant circuit to which the compressor is connected, a map is needed for each air-conditioner, that is, for every type vehicle. This complicates the preparation of maps. Further, estimation of the load torque of the compressor from the map is always required to improve efficiency. This is also complicated.
Further, in an auto air-conditioner, the compressor is controlled by an air controller. In this case, the displacement of the compressor is controlled based on external information such as the temperature in the vehicle passenger compartment, and is not controlled based on torque.
Accordingly, it is an object of the present invention to provide a displacement control apparatus, a displacement control method and a compressor module that accurately controls the compressor displacement based on torque. Another object of the present invention is to provide a displacement control apparatus and a displacement control method in which load torque data of a compressor for controlling the displacement of the compressor can also be used for controlling an engine and it is not necessary to estimate the load torque of the compressor for every type vehicle.
To achieve the object, a displacement control apparatus for controlling the discharge displacement of a variable displacement compressor has a control valve, a first controller, and a second controller. The compressor is incorporated in a refrigerant circuit of a vehicle air conditioner and includes a drive shaft. A load torque is imposed on the drive shaft by driving the drive shaft with an external drive source. A change in the load torque reflects the control of the discharge displacement.
The control valve changes the displacement of the compressor by changing the valve opening degree. The first controller, which is provided outside the compressor, sends a torque setting signal. The torque setting signal indicates a set torque for controlling the discharge displacement of the compressor. The second controller receives the torque setting signal sent from the first controller. The second controller computes an index for changing the opening degree of the control valve based on the torque setting signal so that the load torque of the compressor is changed to the set torque. As a result, the control valve opening degree is controlled to change the displacement of the compressor.
A displacement control method for controlling the discharge displacement of a variable displacement compressor is also provided. The compressor is incorporated in a refrigerant circuit of a vehicle air conditioner and includes a drive shaft. A load torque is imposed on the drive shaft by driving the drive shaft with an external drive source. A change in the load torque reflects the control of the discharge displacement.
The method comprises determining a set torque for controlling the displacement of the compressor outside the compressor, transmitting a torque setting signal indicating the set torque to the compressor, and changing the load torque to the set torque by controlling the discharge displacement of the compressor.
A compressor module comprises a compressor, a control valve in the compressor, and a compressor controller mounted on the compressor.
The compressor forms part of a refrigerant circuit in a vehicle air conditioner. The compressor includes a drive shaft on which a load torque is imposed by an external drive source. The control valve changes the discharge displacement of the compressor by controlling the valve opening degree. The compressor controller receives a torque setting signal indicating a set torque from outside the compressor. The compressor controller computes an index for changing the control valve opening degree based on the torque setting signal so that the load torque is changed to the set torque. The compressor controller sends an instruction to the control valve according to the index. As a result, the control valve opening degree is controlled to control the displacement of the compressor.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.